1. Field of the Invention
The present invention generally relates to an image carrier deterioration degree evaluating device, an image carrier failure predicting device, and an image forming apparatus.
2. Description of the Related Art
Conventionally, when a failure occurs in various machines and apparatuses available in the market, users cannot use them until the repair thereof is completed and are forced to bear an inconvenience. Therefore, it is desirable that an occurrence of a failure be predicted and prevented before the failure actually occurs.
Accordingly, technologies to predict whether a failure occurs in a near future have been considered using an internal condition and an internal signal of a machine or apparatus. In particular, failure predicting technologies for hard disks in computers are in practical use and are widely used.
Although, several failure predicting technologies have been produced for an image forming apparatus such as a copying machine having a complex structure, a highly accurate failure predicting technology is not yet established and only a few have been practiced.
Presently, on the maintenance of such an imaging apparatus, maintenance referred to as preventive maintenance is performed. The preventive maintenance is a type of maintenance approach where maintenance is performed before a failure occurs to minimize a downtime of the apparatus. The preventive maintenance can be roughly divided into time based prevention maintenance and condition based prevention maintenance.
The time based prevention maintenance can be divided into periodic maintenance and age-based maintenance. In the periodic maintenance, a person responsible for the maintenance regularly diagnoses the target apparatus and performs maintenance when a sign of a failure is found. In the age-based maintenance, the maintenance is performed when a specified period of time has elapsed after the start of the use or after the last repair. In either case, a systematic maintenance is performed based on the time.
In the condition based prevention maintenance, the condition of the target apparatus is monitored and, when a sign of a failure is found, the maintenance is performed.
In any of these preventive maintenances, due to the maintenances being performed based on an empirical criterion, there is a failure that leads to a forcedly performed corrective maintenance may occur without being noticed even when the failure is about to occur actually. Also, there is a failure that a component that can still be used for a longer period of time may be replaced by judging from an empirical life expectancy, resulting in requiring a wasteful spending.
Accordingly, technologies to predict an occurrence of a failure by the failure predicting technologies described above have been proposed to perform maintenance before the failure occurs.
For example, Japanese Patent Application Laid-open No. 2005-17874 discloses a method of predicting abnormality occurrence, a state discriminating device, and an image forming apparatus.
The method obtains a plurality of kinds of information relating to the state of the image forming apparatus, calculates an index value D from the information thus obtained, and then determines changes in the state of the image forming apparatus based on the data of changes in the index value D calculated over time, thereby predicting an occurrence of a failure from the index value D.
Various other failure predicting technologies have been proposed, all of which perform prediction by discriminating whether the apparatus is in a predictive state of a failure based on a specified index value.
There have been numerous failure predicting technologies proposed for image forming apparatuses, however, in terms of practicability, prediction accuracy is yet to be sufficient. Therefore, an addition of a parameter highly correlative to the failure is desired.
Meanwhile, in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, a phenomenon referred to as “image deletion” is known to occur. The mechanism of occurrence of the image deletion will now be explained.
In an electrophotographic image forming apparatus, prior to forming an electrostatic latent image on a surface of a photosensitive drum that is an electrostatic latent image carrier, the electrostatic latent image carrier is uniformly charged by a variety of methods. A method utilizing corona discharge is commonly used as the charging method.
However, this corona discharging method generates a large amount of ozone when discharging and requires a high-voltage power supply of about four to ten kilovolts.
In the case of charging devices by corona discharge, corona products such as nitrogen oxide (hereinafter, referred to as NOx) may be produced, which results in an adverse effect on image forming.
More specifically, starting a charging operation generates discharges that consequently form NOx. The NOx reacts with water in the air to produce nitric acid and reacts with metal also to produce metal nitrate.
When the nitric acid or the nitrate forms a thin film adhering on the surface of the electrostatic latent image carrier, an abnormal image in which a part of the image is deleted is produced in a high humidity environment.
The reason is that the resistance of the nitride acid or the nitrate becomes low due to their moisture absorption, whereby the electrostatic latent image formed on the surface of the electrostatic latent image carrier is destroyed. This phenomenon is referred to as image deletion.
In recent years, as disclosed in Japanese Patent Application Laid-open No. 2008-309973, such image deletion is detected and further, to prevent the image deletion, an image deletion reducing operation is performed in which a photosensitive drum is run idly or the moisture on the surface of the photosensitive drum is removed by using a heater.
However, it is known that, if the photosensitive drum itself deteriorates, the effect of the image deletion reducing operation is slow to appear due to unevenness of the surface of the photosensitive drum.
With respect to image forming apparatuses, a highly accurate failure predicting technology is desired to be made. Such a highly accurate failure predicting technology is expected to lead to a substantial reduction in downtime and a reduction in maintenance cost. Particularly, prediction for the failure of a photosensitive drum is important above all.
Various approaches in failure predicting technologies for a photosensitive drum have been proposed and developed for practical use. However, the accuracy is not yet sufficient.
Meanwhile, with a photosensitive drum of an electrophotography image forming apparatus, there is a phenomenon known as image deletion. This is a phenomenon likely to occur after a long time of non-use such as first thing in the morning, while it is not a failure. Various approaches have also been proposed to detect image deletion and to reduce image deletion (to recover from a state of image deletion).
However, it is known that, if the photosensitive drum starts to deteriorate, even with such image deletion recovering approaches, the recovered condition differs from that of a normal element.